I thought April showers brought May flowers. Maybe these showers over the last couple of weeks will bring us June flowers too? While we are grateful for the showers, the rain and storms have presented obstacles for vineyards. This and more is discussed in this edition of the vineyard scouting report. 

Phenology 

At the West Madison Agricultural Research Station (WMARS) in Madison, WI, buds average around E-L* stage 17 (12 leaves separated; inflorescence well developed) for Marquette and Brianna and E-L* stage 13 (6 leaves separated) for Petite Pearl. At the Peninsular Agricultural Research Station (PARS) the Itasca  and Marquette vines are six to eight inch shoots E-L* stage 9 (2 to 3 leaves separated; shoots 2-4 cm long). 

High winds resulted in some minor shoot damage to some vines. There have been reports of trellis wire giving and entire vines stripped from trellising.   

The minimum air temperature recorded at NEWA weather station at WMARS for the early morning of May 28th was 51.2°F. 

*E-L stands for Eichhorn-Lorenz growth stages scale to describe grapevine development. 

Pests

Phomopsis leaf spots were observed across all varieties at WMARS. Primarily, leaves closest to the cordon are showing the greatest levels of infection with a decrease in intensity as you venture outside the canopy. If you want to review what Phomopsis is and how to manage it, feel free to review this article when you are stuck inside due to another rain shower. Black rot was also observed on Petite Pearl and Brianna vines. Our vineyards have not received a fungicide application since Wednesday, May 15th. Daily rain showers and high winds have prevented any possibility of a pesticide application. Grape Disease Models on NEWA indicate Black Rot and Phomopsis infections were logged at WMARS vineyards on May 24, 26, and 27, with predictions for infections on May 28 as well. To view conditions and predicted disease events in your area, consult the Grape Disease Models on NEWA. We are anticipating another fungicide application in the next week or so targeting the pre-bloom stage of the vines.  

We observed some unusual damage primarily on Brianna and some LaCrescent vines (See image below) that was also observed at a vineyard in Vernon County on different cultivars on May 29. This damage was observed on the lower, older fully expanded leaves and was seen in somewhat localized areas in the plot. While we do not have a definite answer on what the culprit is, the fact that large areas of the leaves have been chewed away, without any sign of skeletonization (leaving the veins intact), we suspect that this could be the result of feeding by cutworms. Cutworms could have shown up on southern winds that occurred a couple weeks ago and larvae may now be feeding on leaves at night. We will continue to keep an eye on the damage though as the leaves  are still fully expanded and there is still a decent amount of foliage on the plants, we do not anticipate this feeding having detrimental effect on the plant growth or yield later in the season. 

Growing Degree Day (GDD) Accumulations

Below displays the GDD accumulations from April 1 through May 28 for the past three seasons. Our current season appears to be on track with 2023. This data is collected using the NEWA website. You can visit their “About degree days” page to learn more about the concept of degree days as well as the formulas utilized for calculations. 

Growing degree day accumulation as of May 28, 2024 (April 1 start date; base 50°F BE*) at the WMARS. 

Location	2024	2023	2022
WMARS	441	423	356
PARS	249	255	195

*BE = Baskerville-Emin calculation method

Accumulation of growing degree days (GDD) as of May 28 (Starting April 1) at WMARS and PARS for 2022, 2023, and 2024.

This article was posted in Grapes and tagged Amaya Atucha, Christelle Guédot, Courtney C Meeks, gdd, grape phenology, Grapes, growing degree day accumulations, Growing Degree Days, Leslie Holland, PARS, phenology, vineyard, vineyard scouting, WMARS.